This invention relates to a coated synthetic resin lens and, more particularly, to lenses of high impact resistance with an organic primer coating disposed on the lens base with a surface hard coating on the primer coating, the primer coating improving the abrasion resistance, reducing surface reflection and improving adhesion between the coating layers.
Synthetic resin lenses have become popular substitutes for inorganic glass spectacle lenses since the adoption of standards for such lenses by the U.S. Food and Drug Administration in 1972. The increased use of synthetic resin spectacle lenses results from their advantages over glass lenses, including increased safety, lighter weight, more pleasing appearance, good tintability by dispersed dyes and good processability.
At present, synthetic ophthalmic lenses are prepared primarily using synthetic resin base materials such as polydiethylene glycol bisallyl carbonate resin, otherwise known as "CR-39". CR-39 synthetic base materials are popular because they have good abrasion resistance and are relatively easy to process.
Recently there has been an increased demand for higher quality synthetic resin lenses, specifically, thin synthetic resin lenses made of highly refractive resins. U.S Pat. No. 4,369,298 issued to Y. Kida discloses a synthetic resin lens prepared using a base material formed from a resin of aromatic compounds. In addition, polycarbonate and polymethyl methacrylate resin base materials are available.
One disadvantage of synthetic lenses is that they tend to scratch or scar more easily than glass lenses. In an effort to overcome this disadvantage, improved synthetic products have been developed and several types are now available.
Several methods for providing increased abrasion resistance are also available. These methods include use of silicon, melamine or acrylic resin coatings as abrasion resistant coatings. At present, the abrasion resistant properties of a silicon hard coating are superior to the abrasion resistant properties of coatings formed by other methods. Several silicon-type coating compositions and coating techniques exist and include, for example, those disclosed in U.S. Pat. Nos. 3,986,977; 4,027,073 and 4,442,168, all of which disclose coating compositions of colloidal silica and organopolysiloxane.
In addition, U.S. Pat. No. 4,211,823 discloses coatings derived from silica fine particles, hydrolyzates of silane compounds containing at least one epoxy group and aluminum chelate compounds. Articles having these coatings are also disclosed. U.S. Pat. No. 4,355,135 discloses tintable coating compositions. U.S. Pat. No. 3,984,881 discloses a coating composition of hydrolyzed tetraalkoxysilane compounds, hydrolyzates of alkyltrialkoxysilane and metal catalysts. The metal catalysts can include thiocyanate nitrite, aluminate and carbonate. All of these compositions are coated, heated and cured. Accordingly, synthetic resin lenses having excellent abrasion resistance are provided.
As techniques for providing improved abrasion resistant coatings are developed, the number of synthetic resin base materials that can be used expands. In addition to polycarbonate and polymethyl methacrylate, new base materials having other advantages become available. However, it is difficult to achieve good adhesion properties between the synthetic resin base material and the abrasion resistant coating, a factor which causes severe problems.
The properties of a thin film such as an abrasion resistant coating depends to a great extent on the hardness, viscidity (stickiness), elasticity and flexibility of the film. The abrasion resistance of an abrasion resistant coating also depends on the adhesion properties between the coating and the base material. It must be remembered that scratches in synthetic resin lenses can be caused by numerous factors and that most scratches start small, but deepen and enlarge.
In the case of a base material prepared from a polycarbonate or acrylic resin, primer coatings have been experimentally used to adhere the abrasion resistant coating to the base material. For example, in U.S. Pat. Nos. 4,207,357 and 4,284,685, emulsion primer compositions in which a thermoset acrylic polymer is dispersed in water containing hydroxyethylether are disclosed. These compositions are used as primers for polycarbonate resin base materials.
U.S. Pat. No. 4,405,679 discloses several acrylic and vinyl polymers with substitutent groups that are used as primer coatings. Additionally, the disclosure shows colloidal silica filled with polyorganosiloxane as a major constituent of an abrasion resistant coating.
In view of the problems of adhesion between the layers of synthetic resin spectacle lenses, the patented compositions have several disadvantages. For example, adhesion between the primer coating and the abrasion resistant coating is inferior. Accordingly, selection of proper primer and abrasion resistant coating compositions becomes critical.
Another disadvantage of liquid primer coatings is that they generally have insufficient weatherability and cause the abrasion resistant coating to be gradually peeled off. Emulsion type primer compositions are superior to liquid type compositions with respect to adhesion properties. However, abrasion resistant coating compositions prepared in accordance with the invention have the best adhesion properties.
Furthermore, there is an increasing consumer demand for ophthalmic lenses having reduced surface reflection. In the case of lenses having a reflective index of 1.5, one side of the lens reflects about 4% of the light and both sides reflect about 8%. The reflected light makes a user feel dizzy or causes an image to be blurred. In order to overcome this disadvantage, anti-reflection treatments on synthetic resin lenses as well as on camera lenses are used.
Anti-reflection treatment of synthetic resin lenses has disadvantages. For example, the anti-reflection coating deteriorates severely when subjected to heat cycles of high and low temperatures. This is due to the differences in flexibility and coefficient of thermal expansion between the organic lens and the inorganic thin film anti-reflection coating. In addition, the anti-reflection coating tends to peel following crack generation in the synthetic lens. It is also difficult to improve the adhesion between the synthetic resin lens base material and the interface of the deposited anti-reflection material even by the use of vacuum deposition of the anti-reflection material. For these reasons, synthetic resin lenses having anti-reflection coatings are inferior to inorganic glass lenses in terms of durability.
There are several methods for solving these problems. U.S Pat. No. 4,196,246 discloses an inorganic material of silicon oxide laminated between the base material and the anti-reflection coating in order to improve abrasion resistance and durability. Many products on the market are of this type. A layer of an inorganic material having a thickness between about 0.5 and 3 .mu.m is provided in order to increase the abrasion resistance of the coated anti-reflection film. However, there is then insufficient adhesion between the inorganic coating and the synthetic resin lens base material and, therefore, these products have disadvantages in terms of durability and quality. Specifically, the lenses peel under high humidity conditions caused by sweat or placement in a bathroom. Accordingly, adhesion and durability between the layers is not satisfactory. When the inorganic film is thickened to provide sufficient abrasion resistance, adhesion is reduced as a result of the reduced surface tension of the base material. A further problem arises because synthetic resin lenses having an inorganic film provided by deposition have inferior impact resistance and do not meet FDA impact resistance standards.
As discussed, in order to improve abrasion resistance and keep surface reflection low, abrasion resistant coatings of the type shown in U.S. Pat. Nos. 3,986,997; 4,027,073 and 4,442,168 are provided and inorganic anti-reflection films are deposited on the abrasion resistant coating. However, when the inorganic anti-reflection materials are deposited on synthetic resin lenses having cured abrasion resistant coatings formed of colloidal silica and hydrolyzates of methyltrimethoxyethylsilane as major constituents, cracking occurs in the inorganic film and peeling occurs between the inorganic film and the cured coating.
U.S. Pat. Nos. 4,211,823 and 4,355,135 disclose tintable cured coatings. Anti-reflection coatings of inorganic material can be deposited on the lens, but adhesion between the cured coat and the anti-reflection coating is not sufficient and abrasion resistance deteriorates substantially. Furthermore, the smoothness of the lens surface is sacrificed and peeling or cracking occurs due to the formation of blisters. Accordingly, lenses prepared in this manner are not fully satisfactory.
In addition, abrasion resistance deteriorates when anti-reflection coatings are coated on the abrasion resistant coating. The deterioration of characteristic properties often results from inferior adhesion of the layers of such a hybrid material. The adhesion between the abrasion resistant coating, specifically, the organopolysiloxane film, and the anti-reflection coating is poor because the organopolysiloxane film does not have sufficient affinity with the inorganic material.
Accordingly, it is desirable to provide a synthetic resin lens having improved abrasion resistance, high impact resistance, reduced surface reflection, good durability and good adhesion properties between the inorganic anti-reflection coatings.